White pozzolan composition and blended cements containing same

ABSTRACT

A white pozzolan derived from by-products of manufacturing vitreous low alkali, low iron glass fibers, and to the method for producing the white pozzolan. The invention relates as well to cement compositions based on the white pozzolan, such as white and pigmented blended pozzolanic cements of high durability for use in applications such as white or colored architectural concrete, building materials, and manufactured cementitious products. The white pozzolan also functions as a high performance pozzolan with grey cement.

FIELD OF THE INVENTION

[0001] The present invention relates generally to pozzolanic cements,and more specifically relates to a white pozzolan derived from glassmanufacturing by-products, and to the method for producing the whitepozzolan. The invention relates as well to cement compositions based onthe white pozzolan, such as white and pigmented blended pozzolaniccements of high durability for use in applications such as white orcolored architectural concrete, building materials, and manufacturedcementitious products. Although the white color of the pozzolan and itsconsequent use with white cement can generate great added value, thewhite pozzolan also functions as a high performance pozzolan with greycement.

DEFINITIONS

[0002] As used herein the following definitions shall apply, which areadopted from ASTM C-618: Standard Specification for Coal Fly Ash and Rawor Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete:

[0003] “Pozzolan—A siliceous or siliceous and aluminous material whichin itself possesses little or no cementitious value but will, in finelydivided form and in the presence of moisture, chemically react withcalcium hydroxide at ordinary temperatures to form compounds possessingcementitious properties.

[0004] Class N Pozzolan—Raw or calcined natural pozzolans that complywith the applicable requirements for the class as given herein, such assome diatomaceous earths; opaline cherts and shales; tuffs and volcanicashes or pumicites, calcined or uncalcined; and various materialsrequiring calcination to induce satisfactory properties, such as someclays and shales.

[0005] Class F Fly Ash—Fly ash normally produced from burning anthraciteor bituminous coal that meets the applicable requirements for this classas given herein. This class fly ash has pozzolanic properties.

[0006] Class C Fly Ash—Fly ash normally produced from lignite orsubbituminous coal that meets the applicable requirements for this classas given herein. This class fly ash, in addition to having pozzolanicproperties, also has some cementitious properties.”

BACKGROUND OF THE INVENTION

[0007] In a representative glass fiber manufacturing facility, typically10-20 wt % of the processed glass material is not converted to finalproduct and is rejected as industrial by-product or waste and sent fordisposal to a landfill. This rejected material represents a substantialcost to the industry and also generates a consequent detrimental impacton the environment. While the rejected by-product referred to may havewidely varying physical form, ranging from thick fiber bundles topartially fused fiber agglomerates and shot, it is evident from chemicalanalyses of various samples recovered at different times, that thematerial still has a substantially constant chemical and mineralogicalmake-up. Thus, unlike wastes from many other industrial processes whichtypically have widely varying chemical and mineralogical properties, thewaste from the glass fiber manufacturing process is very consistent incomposition and still benefits from the stringent engineering qualitycontrol applied to the glass-making process itself. This consistency isa major advantage to any potential utilization of the glass fibermanufacturing waste.

[0008] More specifically, the glass formulations of great relevance tothis invention are those of low alkali calcia-alumina-silicacompositions (CaO—Al₂O₃—SiO₂ or “CAS”) typically used for commercialglass fiber manufactured to comply with ASTM D-578. These formulationsare given in Table 1. The compositions are vitreous and by virtue oftheir components have very low levels of discolorants. Thesecompositions are expressed conventionally in terms of the element oxideand are not meant to imply that the oxides, crystalline or otherwise,are present as distinct compounds in the amorphous glasses. TABLE 1Composition Range Component (Element Oxide) (% by Weight) Silicondioxide, SiO₂ 52-62 Aluminum oxide, Al₂O₃ 12-16 Iron oxide, Fe₂O₃0.05-0.8  Calcium oxide, CaO 16-25 Magnesium oxide, MgO 0-5 Sodiumoxide + potassium oxide (Na₂O + K₂O) 0-2 Boron oxide, B₂O₃  0-10Titanium dioxide, TiO₂   0-1.5 Fluorine, F₂ 0-1 MineralogicalComposition (XRD) Amorphous (glassy)

[0009] Several features are immediately evident from inspection of thedata in Table 1. First, the general chemical and mineralogicalcomposition of the glass fiber material is very similar to amorphous(glassy) calcium alumino-silicate materials, such as blast-furnace slagand Class C fly ash, that are commonly used as cementitious orpozzolanic admixtures in portland cement concrete; second, the alkali(Na₂O+K₂O) content of the glass is very low (0 to 2%); and third, withtheir inherently low iron contents (0.05 to 0.8%), the glasses havelittle or no color. Low alkali content and chemical consistencydifferentiates the glass fiber manufacturing waste from post consumerwaste glass, for example container bottles and flat glass, that havewidely varying chemical composition, generally high alkali content, andin the case of container/bottle glass are highly colored.

[0010] Conventionally, white portland cement is used in a variety ofapplications, including but not limited to: white or light coloredarchitectural concrete; precast concrete panels; cast stone monumentsand statuary; ornamental landscaping; decorative flooring tiles andterrazzo; wall cladding, stuccos and plasters; tile grout; caulk andwhite cement paint.

[0011] White portland cement by itself does not have good durability,particularly under service conditions where it is exposed to attack bysulfate solutions and other aggressive chemicals. This is because thechemical composition of white cement is different from gray Portlandcement in order to obtain the desirable white color. The main differenceis that white cement has a very low iron content which during themanufacturing process leads to the formation of much higher tricalciumaluminate C₃A content in the finish clinker. Typically during cementmanufacturing, C₃A reacts with iron oxide to form tetracalciumaluminoferite (C₄AF). The lack of iron oxide in white cement results inhigh levels of tricalcium aluminate that are the reason for the wellknown susceptibility of white cement to chemical deterioration whenexposed to an environment that is rich in sulfate. Such an environmentcan be found in many soils and in seawater. A high C₃A content can alsocontribute to the increase in volume changes that can result in theformation of cracks in hardened concrete.

[0012] Cementitious and pozzolanic admixtures used with portland cement,such as blast-furnace slag, fly ash, silica fume and metakaolin, arecharacteristically fine particulate powder materials that are comparablein fineness to portland cement. In addition to improving the economicsof production through cement replacement, these “supplementary cementingmaterials” are also well known to improve the long term durability ofcement and concrete products, for example by reducing deterioration dueto attack by aggressive chemical media, such as sulfate, and expansiondue to reactions between the aggregates and the cement alkalis(so-called “alkali-aggregate reaction” or AAR).

[0013] These pozzolans, however, have chemical components thatinevitably impart an undesirable dark color to white cement that negatesthe reason for using the material. For this reason, use of thearchitecturally desirable white cement has been somewhat limited toapplications where there is no likelihood of exposure to sulfate andother aggressive chemicals. This is unfortunate because major marketsfor white and light colored concrete and concrete products exist in thecoastal regions where exposure to high sulfate containing soils andseawater spray are likely.

[0014] Another additive that has been used in white cement ismetakaolin. See for example U.S. Pat. Nos. 6,007,620, and 6,033,468,disclosing an interground white blended cement based on metakaolin.Metakaolin however, aside from its relatively high costs, differs fromthe pozzolan of this invention, in typically imparting a cream topinkish tone to white cement and in having very high water demand,rendering it of limited commercial value in the area of presentinterest.

SUMMARY OF INVENTION

[0015] Now in accordance with the present invention the inventors havefound that once it is ground to a powder of suitable fineness, the glassfiber waste discussed above can effectively function as a reactivepozzolanic admixture for use in portland cement-based building materialsand products, such as concrete, mortars and grouts.

[0016] The inventors have also found that, unlike other cementitious andpozzolanic admixtures, such as blast-furnace slag, fly ash and silicafume which are characteristically dark in color, the finely ground glasspozzolan (which retains the vitreous nature and chemical composition ofthe fiber feed) is white in color. This white color makes the glasspozzolan highly desirable as a pozzolanic admixture for use with whiteportland cement, an application that is not suitable for the darkcolored pozzolans.

[0017] According to a process aspect of this invention, glass fiberwastes are converted into high quality filler and pozzolan products, byshredding long entangled strands of glass into short fibers, adjustingthe moisture content of the short fibers, grinding the short fiber, andclassifying the ground material to produce a uniform high qualityproduct with precise control over the maximum particle size and particlesize distribution. Because of its physical characteristics, this productwill at times herein be referred to as “white VCAS pozzolan”, the “VCAS”being a reference to its production from fibers of “vitreouscalcium-alumino-silicate” glass. The white VCAS pozzolan has areflectance value of at least 80 as measured by a Technibrite TB-1Ccalorimeter according to the ISO 2467, 2471 method.

[0018] Several options are available for use of the white VCAS pozzolanof the invention in the cement and concrete industry: (a) it can beadded as a separate pozzolanic component to the cementitious mixture(concrete, mortar, grout, etc.) meeting the requirements of ASTM C-618;(b) it can be blended in the powder form at the manufacturing plant withwhite portland cement to produce a blended cement meeting therequirements of ASTM C-595 or C-1157; and (c) it can be interground withwhite portland cement clinker and the appropriate amount of gypsum forset control at the finish mill. (The white clinker can e.g. be of TypeI, Type II, Type III, Type IV, or Type V ASTM C-50 cements) In thesefunctions, the new white VCAS pozzolans compare favorably withsupplementary cementing materials such as fly ash, blast furnace slag,condensed silica fume, and metakaolin that are routinely sold into thecement and concrete additives markets. When blended with a portlandcement, the white VCAS pozzolan will generally be present as 10 to 30%by weight of the total composition, with 10 to 30% weight beingpreferred. Those skilled in the art will also recognize that all ofthese applications for the white VCAS pozzolan are equally suited togrey portland cement, albeit without the advantage of light color.Accordingly there is no implied limitation of the use of the whitepozzolan only in white cement systems. Where used in a blend withcement, conventional functional cement additives can also be present,such as accelerators, retarders, water-reducers/plasticizers, corrosioninhibitors, and pigments.

[0019] As a consequence of their fine particulate granulometry and a lowsurface absorptivity that provides low water demand, the VCAS pozzolanscan markedly improve the compaction and cementing efficiency of cementand concrete mixtures in which it is used. As those skilled in the artwill recognize, this has significant advantages for a designer of cementand concrete materials and products, because sufficient fluidity forplacement can be achieved at a lower water content, and hencewater-to-cement (w/c) ratio, thus allowing for either an increase instrength for a given cement factor, or a reduction in the cement contentfor a given strength. In addition, in common with other siliceouspozzolanic admixtures, the VCAS pozzolans react chemically in thecementitious matrix to consume excess calcium hydroxide, Ca(OH)₂,produced from the hydration of the tricalcium and dicalcium silicates(C₃S and C₂S) in portland cement, converting it to calcium silicatehydrate (C≦S≦H) that functions as additional binding agent. Theconversion of the calcium hydroxide to supplementary C—S—H binder servesto improve the long-term strength potential of cement and concreteproducts and materials, while at the same time improving theirdurability and service life towards deterioration in the presence ofaggressive chemical media such as sulfate-containing soils and water.

[0020] As discussed above, the chemical composition of the raw materialsused for the manufacture of white portland cement production is modifiedto achieve the light color, usually by reducing the iron and magnesiumcontents. As a result, white portland cements typically have highertricalcium aluminate phase (C₃A) contents than grey portland cements, asis shown in Table 2 based on information provided by the Portland CementAssociation. TABLE 2 Type of Portland Cement White Type I Grey Type IComponent, % SiO₂ 22.5 20.5 Al₂O₃ 4.5 5.4 Fe₂O₃ 0.4 2.6 CaO 66.3 63.9MgO 1.0 2.1 SO₃ 2.8 3.0 Na₂O eq. 0.17 0.61 Loss on ignition 1.7 1.4Potential Compounds, % C₃S 60 54 C₂S 19 18 C₃A 11 10 C₄AF 1 8

[0021] It is well known that it is the C₃A content of a portland cementthat is a measure of its susceptibility to attack by sulfate. Therefore,the higher content of this compound in white cement (C₃A=11-12%) meansthat it will be more susceptible to this form of deleterious chemicalattack than common Type I grey cement (C₃A=8-10%). Historically, thischemical susceptibility has been one of the weaknesses of white portlandcement that has limited its further growth into the market place, forexample into areas where there is significant sulfate content in soilsor in areas close to the ocean. While it is common practice to usepozzolanic admixtures such as fly ash, silica fume or blast-furnace slagto improve the durability of grey portland cement to deleteriouschemical attack, these pozzolanic materials all impart a dark colorationto the cement matrix and are therefore unsuitable for use where a whitecolor is required architecturally. Therefore, the availability of awhite pozzolan is highly desirable for the production of more durablepozzolanic white cements.

BRIEF DESCRIPTION OF DRAWINGS

[0022] In the drawings appended hereto:

[0023]FIG. 1 is a schematic block diagram illustrating a process whichmay be used to prepare the white VCAS pozzolan of the present invention;and

[0024]FIG. 2 is a graph showing expansion data for a blended cementprepared pursuant to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0025] According to the process aspect of this invention, glass fiberwastes are converted into high quality filler and pozzolan products, bya shredding long entangled strands of glass into short fibers, adjustingthe moisture content of the short fibers, grinding the short fiber, andclassifying the ground material to produce a uniform high qualityproduct with precise control over the maximum particle size and particlesize distribution.

[0026] The process of glass manufacturing entails melting a mixture ofcarefully selected oxides, then cooling the molten material to producethe desired size, shape, and characteristics (e.g., container glass,flat glass, optical glass, fiber glass, etc.). The carefully selectedingredients for glass manufacturing are typically based on specificformulations of three material types: i.e., glass formers, glassmodifiers or fluxes, and stabilizers. Glass formers comprise the majorcomponents of glass and most commonly consist of silicon dioxide in theform of sand and aluminum oxide in the form of alumina. Boron oxide isanother common glass former component found in some formulations. Glassmodifiers or fluxes lower the melting temperature and alter theviscosity of the glass melt and consist primarily of alkaline earthmetal and alkali metal oxides, typically derived from the raw materialscalcium carbonate, sodium carbonate and potassium carbonate. Stabilizersare added to make the glass strong and resistant to water and chemicalattack. Low alkali glass, such as many of the formulations typicallyused for the manufacture of high performance glass fiber, is speciallyformulated for resistance to high temperatures and corrosive substances,in addition to having high physical strength and flexibility.

[0027] The process of glass fiber forming involves feeding molten glassfrom a high temperature furnace through a series of bushings containingthousands of accurately dimensioned holes or tips. Fine individualfilaments of glass with diameters typically in the range 20-60 micronsare drawn mechanically downward from the bushing tips, cooled andbrought together to form bundles or strands of glass fibers. In theprocess of forming glass fibers, a significant amount of wastage isgenerated, mostly in the form of irregular, entangled long strands andbundles, often with nodules from partial fusion. The waste strands andbundles can be many tens of feet in length and are in a form that is notconducive to easy handling and processing by conventional means. Thiswaste material is typically cooled by water quenching and shipped to alandfill for disposal. According to this invention a large amount ofthis waste glass fiber material can be processed and converted into highperformance industrial products.

[0028] A typical process useful in the invention is shown schematicallyin FIG. 1. In the first step of the present process, the glass fiberwaste (feed stock 12) is collected and placed in a containment area forde-watering and trash removal. Water used to cool the waste fiber streamis allowed to drain off the fibers and is collected and transferred tothe wastewater treatment system. Incidental trash objects are manuallyremoved from the bulk waste materials to allow for further processing.

[0029] In the second step of the process, the moist waste glass fiberbundles are processed by a shredder at fiber shredding through ashredder 14 to reduce the fiber length from infinitely long entangledstrands to short fibers (typically less than 5 mm) for subsequentprocessing. The shredding stage consists of processing the entangledstrands through a rapid rotating mandrel with protruding cutting knives.Stationary cutting edges are also located opposite the rotating mandrel.The fast cutting action of the knives snaps the entangled glass bundlesand strands into the desired short individual fibers. A screen enclosurearound the rotating mandrel is used to retain the large entangledstrands and ensure shredding into short fibers.

[0030] In the third step of the process (fiber drying 16), the moisturecontent of the shredded short fibers is adjusted prior to furtherprocessing using dry and heated air. The moisture content is controlledto a predetermined specific range to optimize the subsequent grindingprocess. Generally the moisture content should be less than 10% byweight, and is preferably less than 2% by weight. In a very typicalinstance the moisture content is from 0.5 to 1.0% by weight.

[0031] In the fourth step of the process, the shredded short fibers aresubjected to fine grinding 16 by being processed through an attritionmill, preferably in a vertical attrition mill such as a stirred oragitated ball mill. The short fibers and the ground glass are veryabrasive materials. Abrasion of commonly used stirred mill componentsnot only contaminates the product, it also reduces the grindingefficiency. In the present process the mill uses a rotation shaft andarms that agitate the grinding media and create both impact and shearingaction, resulting in efficient product size reduction. The rotating armsare covered with replaceable leading-edge ceramic protectors composed ofdie cast and heat-fused alumina. The wall of the attrition mill is alsolined with abrasion-resistant alumina to further minimize productcontamination from the metal components in the mill. The mill uses thehighest quality high alumina grinding media consisting of ⅛″ to ⅜″diameter balls. The effectiveness and efficiency of the attrition millare greatly enhanced by the die-cast, heat-fused leading edge protectorattachments of the agitator arms. Energy inputs used in this grindingprocess are at least 100 kW-hrs/ton of feed fibers and typically are inthe range of 100 to 200 kW-hrs/ton of the feed fibers.

[0032] The attrition mill is typically operated with continuous feed anddischarge, although if desired it can alternatively be operated in abatch mode. The discharged grinding media and product are separated instage five of this process using a vibratory screen with 80 to 100 meshopenings. The grinding media and oversize glass comminution products arereturned to the attrition mill for continuous processing. The groundglass product passing the screen is conveyed to an air classificationsystem for product refinement.

[0033] In step six of the invention (fine powder classification 18), theground glass product is processed through a high-performance,dual-cyclone, dry air classification system. This stage is used tocontrol the fineness and particle size distribution of the product fromfine grind to low-micron range depending on the required specification.Particles larger than the maximum allowable are returned to theattrition mill for further grinding. The use of an air classificationsystem in this stage allows for precise control over the maximumparticle size and ensures the production of a uniform product. The airused in classification is vented through a filter fabric dust collector(Air emission control system 20). Ultra fine particles collected in thefilter fabric can be blended with the final product (Blending Packaging22).

[0034] The final classified white VCAS pozzolan product will generallyhave a particle size distribution such that at least 95% of theparticles by weight have an equivalent spherical diameter (E.S.D.) ofless than 45 μm (microns). Typically 95% by weight may be less than 25μm; (typical median size around 9 μm); and for many applications themilling and classification will provide an end product where 95% byweight of the particles are of less than 10 μm E.S.D. (a typical mediansize here is around 3 μm); and in other instances the said end productcan have P.S.D.'s where 95% of the particles by weight are less than 5μ, or even less than 3 μ.

[0035] The finely ground white VCAS pozzolan product as produced by thisprocess is characteristically of a blocky, almost equi-dimensionalparticle shape, with no evidence of residual high aspect ratio fibers.The aspect ratio of the particles will typically average less than 2:1,with the aspect ratio becoming smaller as the average particle sizebecomes smaller as a result of the milling and classification asdiscussed above. The finely ground powder product yielded by theinvention can be packaged in bags or sold in bulk for industrial fillerand concrete applications. This product can serve as a replacement tohigh priced white fillers and super pozzolans. The final product fromthe process contains substantially no particles which NIOSH defines as“respirable fibers,” i.e., particles which are greater than 5 μm inlength and less than 3 μm in diameter with an aspect ratio of greaterthan or equal to 5:1.

[0036] The invention is further illustrated by the following Examples,which are indeed to be considered exemplary of the invention, and notdefinitive thereof.

EXAMPLE 1 Preparation of White VCAS Pozzolans and Blended PozzolanicCements

[0037] To facilitate an evaluation of their potential pozzolanicproperties, by-product glass fiber waste materials having compositionsas shown in Table 1 were ground to fine powders with a variety ofdifferent particle size distributions or finenesses. This was carriedout using both laboratory and pilot-scale equipment in a multi-stageprocess involving drying, comminution, screening, and high efficiencyair classification, the object being to have no residual high aspectratio particles (shards) in the powder products. Representativesub-samples of the ground VCAS product materials from this process werecharacterized for their granulometry properties, some illustrativeexamples of which are shown in Table 3. TABLE 3 SSA Median D95 PozzolanID (m²/kg) (μm) (μm) GP1 269 nd 50 GP2 560 12  30 GP3 580 10  30 GP4 6869 25 GP5 788 6 20 GP6 956 3 10 GP7 >1200  1  3

[0038] The specific surface area (SSA) of the VCAS pozzolan powders wasdetermined by the Blaine air permeability method according to ASTMC-204. The results in Table 3 show that the range of specific surfaceareas for the prepared VCAS pozzolan powders was 250 to greater than1200 m²/kg. The corresponding particle size distribution, medianparticle size, and D95 (particle size with 95% of the particles finer)of the products, were determined by the laser interferometer techniquein aqueous dispersion using Microtrac® X100 or Coulter LS® particle sizeanalyzers. The median particle sizes of the VCAS pozzolan productsranged from 1 μm (microns) to 12 μm, with corresponding D95 valuesranging from 3 μm (microns) to 50 μm. The specific gravity of the VCASpowders, as determined by the Le Chatelier method (ASTM C-188), was 2.57cm²/g.

[0039] Examination of the VCAS powders at high magnification by scanningelectron microscopy (SEM) confirmed that, as is typical of such groundmaterials, all the VCAS pozzolan samples were substantially blocky inparticle shape. There was no sign of residual high aspect ratioparticles. X-ray powder diffraction (XRD) analysis of the VCAS powdersconfirmed that that they were all essentially amorphous in structure.

[0040] Under the ASTM C-618 standard, based on the chemical composition(SiO₂+Al₂O₃+FeO₃), the VCAS pozzolans fall in the range of “Class N”pozzolans and at the low end of the range for “Class F” fly ashes.Applicable standards for the blended pozzolanic cements containing theVCAS pozzolans would include ASTM C-1157: Standard PerformanceSpecification for Hydraulic Cement; and ASTM C-595: StandardSpecification for Blended Hydraulic Cements.

[0041] The tri-stimulus color/brightness of the VCAS pozzolan powderscompared with white portland cement (Federal White, Ontario) wasdetermined according to ISO 2467, 2470, 2471 by the Technibrite TB-1Cmethod, as follows: 100% WPC=75.5; GP6=84.2. Cement pastes prepared atw/c=0.4 with 100% white portland cement (WPC) and a 90:10 blend of whiteportland cement and VCAS pozzolan GP6 gave TB-1C values of 62.3 and70.1, respectively. Thus, the VCAS pozzolans have a color/brightnessthat is somewhat whiter and brighter than white portland cement itself.

[0042] Blended pozzolanic cements were then prepared by intimatelyblending the ground VCAS pozzolan powders with commercial portlandcement in various ratios in the range 10-30% by weight VCAS pozzolanreplacing cement: namely, 90:10, 80:20, 70:30. The commercial portlandcements used in these blends covered a range of alkali contents,including a low alkali (PC 1), moderate alkali (PC2), and high alkali(PC3).

EXAMPLE 2 Pozzolanic Activity (Accelerated) of White VCAS Pozzolans

[0043] The pozzolanic performance of the various VCAS pozzolans fromExample 1 were evaluated in portland cement mortars using the ASTMC-1240 method (Table 4). This method is an accelerated techniquecommonly used the evaluation of silica fume pozzolans and provides a“pozzolanic activity index” as a measure of the reactivity of thepozzolan. The method involves preparing test mortars to standard flow(100-115%) in which 10% by weight of the portland cement is replacedwith the test pozzolan. The fresh mortar is cast into 2-inch cubes whichare then allowed to cure, first for 24 hours at 100% relative humidityat 23° C., and then for 6 days in airtight container at 65° C., prior tomeasurement of compressive strength. The pozzolanic activity index ofthe pozzolan is then calculated as the ratio of the strength of the testmortar to the strength of a control (100% portland cement) mortarexpressed as a percentage.

[0044] The test results collected in Table 4 show that mortars preparedwith all of the VCAS pozzolans comfortably exceed the strengthrequirements of 85% of control as specified in ASTM C-1240. As istypical of other pozzolans, the pozzolanic reactivity of the VCASpozzolans generally improve as the fineness increases. However, underthe conditions of test, the finer grade pozzolans typically have agreater demand for water to reach standard flow. This results in ahigher water to cement (w/c) ratio and somewhat lower strengthpotential. Tested under ASTM C-1240 protocols, the results for the VCASpozzolans are comparable to or slightly better than silica fumes andmetakaolins that have much high water demand to meet standard flow.TABLE 4 Pozzolanic SSA Mortar Strength (psi) Activity Index Sample ID(m²/kg) Control PC Test PC/GP (% Control) 9010PC1/GP1 269 4,336 4,292 99 9010PC1/GP2 560 4,367 4,585 105 9010PC1/GP3 580 4,365 4,988 1149010PC2/GP4 686 5,046 5,127 102 9010PC2/GP5 788 5,046 5,455 1089010PC1/GP6 956 4,485 4,640 103

EXAMPLE 3 Properties of Blended Portland-VCAS Pozzolan Cements

[0045] Further comparison of the performance of the blended portlandpozzolanic cements prepared with the VCAS pozzolans described in Example1 was conducted according to ASTM C-618: Standard Specification for CoalFly Ash and Raw or Calcined Natural Pozzolan for Use as a MineralAdmixture in Concrete (Table 5). In this test method, test mortar wereprepared according to ASTM C-109 protocols in which 20% by weight of theportland cement was replaced with the test pozzolan, with water added toproduce a standard flow (110-115%). Water requirement for the testmortars was typically 95-98% of control, comfortably within the limit of105% specified for F and C pozzolans and substantially less than the115% specified for N pozzolans in ASTM C-618. The fresh mortar was thencast into 2-inch cubes and allowed to cure at 21° C. in limewater untiltime of test at 7, 14 or 28 days. The strength activity index of thepozzolan was then calculated as the ratio of the strength of the testmortar to the strength of a control (100% portland cement) mortarexpressed as a percentage.

[0046] The test results collected in Table 5 show that 8020 blendedcement mortars prepared with all of the white VCAS pozzolans comfortablyexceed the strength requirements of 75% of control as specified in ASTMC-618. The 8020PC1/GP5 blended cement mortars markedly outperformed thecontrol portland cement mortar (123% of control at 7 and 149% of controlat 28 days); and the 8020PC1/GP6 blended cement mortar outperformed thecontrol mortar at 28 days (115% of control). The white VCAS pozzolansexceed the performance of most high quality fly ashes and naturalpozzolans. Other important characteristics of the cement systems, suchas time of set or water requirement, where not adversely affected. It issignificant to note that while these tests are conducted underconditions of standard flow, the higher surface area GP5 and GP6pozzolans (788 and 956 m² kg) do not require the large amount of extrawater that are common with other high surface area pozzolans such assilica fume and metakaolin. TABLE 5 Mortar Curing Strength (psi)Strength SSA Age Control Test Activity Index Sample ID (m²/kg) (Days) PCPC/GP (% Control) 8020PC1/GP5 788 14 4,513 5,570 123 28 4,811 7,180 1498020PC2/GP5 788  7 5,005 3,766  75 28 6,422 6,151  95 8020PC1/GP6 956  74,624 3,847  83 28 5,047 5,802 115

EXAMPLE 4

[0047] A further series of blended pozzolanic cement mortars wasprepared according to the ASTM C-109 protocol in which 30% of the whiteVCAS test pozzolan replaced portland cement, rather than the 20%replacement prescribed in ASTM C-618 described above. The results ofthese tests (Table 6) show that even at the higher cement replacementlevel, the 7030PC1/GP6 blended cement still comfortably exceeded theASTM C-618 requirement of 75% of control at curing ages of both 7 and 28days. At a cure age of 28 days, the strength activity index of7030PC1/G6 blended cement mortar was 105%, showing that the blendedcement outperformed the 100% cement control mortar. It is alsonoteworthy that, even with 10% less portland cement, the 7030PC1/P6blend had comparable performance to the 8020PC1/GP6 TABLE 6 MortarCuring Strength (psi) Strength SSA Age Control Test Activity IndexSample ID (m²/kg) (Days) PC PC/GP (% Control) 7030PC1/GP6 956  7 4,6244,064  88 28 5,047 5,314 105

EXAMPLE 5 Improvement of Sulfate Resistance

[0048] The efficiency with which the white VCAS pozzolan of theinvention reduces the expansion caused by attack by sulfate was testedaccording to the ASTM C-1012 method using mortar bars prepared with 20%by weight of the VCAS pozzolan substituting for white portland cement atw/c=0.485 and a flow of 95-105% of control.

[0049] Illustrative expansion data for the GP5 pozzolan (SSA=788 m²/kg)mortars are given in Table 7 and shown graphically in FIG. 2. It can beseen that significant expansion in the 100% white portland cementcontrol mortar began at around 100 days and continued until the samplecompletely disintegrated before 290 days. By comparison, in the mortarwith 20% GP5 VCAS pozzolan substituting for the white cement, verylittle expansion had occurred out to well over a year (405 days). TABLE7 Exposure Age Mortar Expansion (Days) 100% WPC Control 80:20 WPC/GP5  70.0200 0.0100  28 0.0363 0.0238  56 0.0425 0.0295 128 0.0623 0.0335 2240.5593 0.0608 290 1.0445 0.0632 405 N/a* 0.0640

[0050] These results for the blended white pozzolanic cement system maybe compared favorably with those that can be achieved with a sulfateresisting ASTM C-150 Type V grey portland cement and/or blends of a TypeI grey portland cement with colored pozzolans such the best guality fly,ashes, blast-furnace slag, metakaolin or silica fume. This confirms thatthe white VCAS pozzolan can markedly improve the chemical durability ofwhite portland cement, while still retaining the architecturallydesirable white color.

[0051] While the present invention has been described in terms ofspecific embodiments thereof, it will be understood in view of thepresent disclosure, that numerous variations upon the invention are nowenabled to those skilled in the art, which variations yet reside withinthe scope of the present teaching. Accordingly, the invention is to bebroadly construed, and limited only by the scope and spirit of theclaims now appended hereto.

What is claimed is:
 1. A white pozzolan for use in blending withportland cement in concrete applications, comprising a finely groundvitreous calcium aumino-silicate (CaO—Al₂O₃—SiO₂) low alkali, low ironcontent glass derived from glass manufacturing by-products.
 2. Acomposition in accordance with claim 1, wherein said glass by-productsare waste glass fibers having low alkali and low iron content, and lowlevels of discolorants, whereby said composition may be effectivelyblended with said portland cement for use in white and colored concreteapplications.
 3. A composition in accordance with claim 2, having analkali content by weight of not more than 2% as (Na₂O+K₂O), an ironcontent by weight of not more than 0.8% as Fe₂O₃, and which issubstantially white in color.
 4. A composition in accordance with claim3, wherein said pozzolan is a powder having a reflectance value of atleast 80 as measured by a Technibrite TB-1C calorimeter according to theISO 2467, 2471 method and a blocky, relatively equi-dimensional particleshape with substantially no residual high aspect ratio fibers.
 5. Acomposition in accordance with claim 4, wherein the said pozzolan has aP.S.D. such that at least 95% by weight of the particles are of lessthan 45 microns E.S.D.
 6. A composition in accordance with claim 4,wherein the said pozzolan has a P.S.D. such that at least 95% by weightof the particles are of less than 25 microns E.S.D.
 7. A composition inaccordance with claim 4, wherein the said pozzolan has a P.S.D. suchthat at least 95% by weight of the particles are of less than 10 micronsE.S.D.
 8. A composition in accordance with claim 4, wherein the saidpozzolan has a P.S.D. such that at least 95% by weight of the particlesare of less than 5 microns E.S.D.
 9. A composition in accordance withclaim 4, wherein the said pozzolan has a P.S.D. such that at least 95%by weight of the particles are of less than 3 microns E.S.D.
 10. Acomposition in accordance with claim 4, wherein the average aspect ratioof the particles of the pozzolan is less than 2:1.
 11. A blendedpozzolanic cement produced by blending with portland cement, from 5 to40% by weight of the total composition of a fine white pozzolancomprising finely ground vitreous low alkali low iron glass derived fromglass manufacturing by-products.
 12. A blended cement in accordance withclaim 11 which is substantially white; said cement having a reflectanceof at least 80 on an “Rd” scale measured on a Hunter Lab calorimeter.13. A white pozzolanic cement produced by intergrinding of a vitreouslow alkali, low iron pozzolan derived from glass manufacturingby-products with white portland cement clinker and white gypsum.
 14. Araw feed for white cement clinker production comprising a finely groundvitreous low alkali, and low iron content glass derived from finegrinding of glass fibers.
 15. A white pozzolanic cement in accordancewith claim 13, wherein said white clinker is selected from one or moremembers of the group consisting of Type I, Type II, Type III, Type IV,or Type V ASTM C-150 cements.
 16. A colored pozzolanic cement comprisingthe white cement of claim 12 together with an admixed pigment.
 17. Ablended pozzolanic cement in accordance with claim 11, furthercomprising one or more functional cement additives selected from thegroup consisting of accelerators, retarders,water-reducers/plasticizers, corrosion inhibitors, and pigments.
 18. Aprocess for converting glass fiber wastes into high quality filler andpozzolan products, comprising shredding long entangled strands of lowalkali and low iron content vitreous glass fibers into short fibers,adjusting the moisture content of the short fibers, grinding the shortmoisture adjusted fibers, and classifying the ground material to producea uniform high quality substantially white product with precise controlover the maximum particle size and particle size distribution.
 19. Aprocess in accordance with claim 18, wherein the waste glass fibers haveby weight an alkali content of less than 2%, and an iron content of lessthan 0.8%.
 20. A process in accordance with claim 19, wherein saidshredding provides short glass fibers of less than 5 mm.
 21. A method inaccordance with claim 20, wherein said shredded and moisture adjustedshort fibers are ground in a vertical attrition mill using an energyinput of at least 100 kW/hrs/ton of said fibers.
 22. A process inaccordance with claim 21, wherein said shredded short fibers have anadjusted moisture content of less than 10% by weight.
 23. A process inaccordance with claim 22, wherein said shredded short fibers have anadjusted moisture content of less than 2% by weight.
 24. A process inaccordance with claim 22, wherein said shredded short fibers have anadjusted moisture content of 0.5 to 1.0% by weight.